1) Field of the Invention
This invention relates to a metal vapor discharge lamp suitable for use in the fields of photochemical reactions, curing of paints and inks, and the like.
2) Description of the Prior Art
Ultraviolet rays having a wavelength region of 280-400 nm are generally used in the fields of photochemical reactions, curing of paints and inks, and the like. In order to increase the radiant intensity of the ultraviolet rays of such a wavelength region, it is effective to fill a light-emitting tube with iron having a continuous spectrum in the wavelength region of 350-400 nm together with mercury.
However, in conventional metal vapor discharge lamps having light-emitting tubes in which iron is filled therein, iron deposits on the inner walls of their light-emitting tubes as the operation time goes on, thereby forming a thin film. Therefore, conventional metal vapor discharge lamps have the problem that the quantity of iron which contributes to the light emission becomes smaller and the through the light-emitting tubes, so that the radiant intensity of the ultraviolet rays s decreased to a great extent as time goes on.
In addition, when an electrode interval L is as long as 750 mm or greater in particular, namely, the light-emission length is longer, the following problem arises. Namely, even f such a discharge lamp is lighted in a horizontal direction, the intensity of the emission spectrum of iron becomes uneven along an axial direction of its light-emitting tube. The reason of this nonuniform phenomenon of the intensity is that iron filled within the light-emitting tube distributes unevenly therein and concentrates only in its central portion or one side. The occurrence of such an nonuniform phenomenon is accompanied by the disadvantages that a photochemical reaction from the transmitted light will undergo an uneven reaction, and irregular curing may occur upon the curing of paints or inks.